84 NERVOUS SYSTEM. 



the facial, the auditory, the par vagum, the glosso-pha- 

 ryngeal, and the great hypoglossal. 



Q. Is the adhesion of these nerves to the brain strong? 



/?. No; they are so weak as to be torn by the raising 

 of the pia mater. 



Q. What nerves arise from the spinal marrow? 



*&. The cervical, eight pairs in number; the dorsal, 

 twelve pairs; five sets of lumbar; five or six sacral; in all 

 amounting to thirty or thirty-one pairs. The spinal nerve, 

 so called, which penetrates the cranium and again emerges 

 from it, also arises from the spinal marrow. 



Q. Are the nerves elongations of the brain? 



/?. They are not; they are formed cotemporaneously 

 with the brain, and are independent organs communicat- 

 ing with the brain. 



Q. What has given rise to the opinion of the decussa- 

 tion of all the nerves? 



Jl. The supposition is founded on the fact, that paralysis 

 occurs on the side of the body opposite to the hemisphere 

 of the brain that is injured. 



Q. Does anatomy prove this decussation? 



Ji. It does not. 



Q. Does palsy in the motion of a limb necessarily in- 

 volve loss of sensation in the member? 



#. It rarely suspends sensibility. 



Q. On what do discordant hearing and vision often 

 depend? 



Jl. Frequently on a diseased condition of the organ af- 

 fected, which does not involve a morbid state of the brain. 



Q. What membranes are found about the nerves? 



&. The dura mater invests them to their exit from the 

 brain and spine. The tunica arachnoides envelopes thr 



